Plug rolling mill



Nov. 27, 1956 A. F. KRITSCHER PLUG ROLLING MILL 6 Sheets-Sheet 1 Filed March 6, 1952 A. F. KRITSCHER PLUG ROLLING MILL Nov 27, 1956 6 Sheets-Sheet 2 Filed March 6, 1952 I l I I l FIEJQ Nov. 27, 1956 A. F. KRITSCHER 2,771,800

PLUG ROLLING MILL Filed llarch 6, 1952' 6 Sheets-Sheet 3' fli/VDPEW F mama/5Q,

Nov, 27, 1956 A. F. KRITSCHER PLUG ROLLING MILL s Sheets-Sheet 4 Filed March 6, 1952 Nov. 27, 1956 KRLTSCHER 2,771,800

PLUG ROLLING MILL Fil'd March 6. 1952 e, Sheets-Sheet 5 27, 1956 A. F. KRITSCHER 2,771,806

PLUG ROLLING MILL Filed March 6, l952 6 Sheets-Sheet 6 United States PLUG ROLLING MHJL Andrew F. Kritseher, Pittsburgh, Pa., assignor to United States Steel Corporation, a corporation of New Hersey Application March 6, 1952, Serial No. 275,119

Claims. (Cl. 80-11) This invention relates to improvements in plug rolling mills of plug rolling.

In the art of seamless tubing manufacture, a plug rolling mill is a non-reversing two-high roll stand for rolling pierced billets after they have been reheated. On its entry side the mill has a trough for receiving pierced billets and a pusher for moving them singly into the rolls; on its delivery side it has a guide table, a plug or mandrel bar, and support means for the latter. This bar carries a removable plug which during rolling is situated within the pierced passage through the billet directly between the work rolls. After the first pass of a billet through the mill, the plug is removed, the work rolls are separated, and the billet is backed out with stripper rolls, rotated 90 on its longitudinal axis, and given another pass. The billet is backed out similarly as it leaves the mill after the second pass. The plug must be removed and cooled after every pass and replaced before the next pass. Although I am aware of earlier patents which show mechanical plug handling mechanisms, in practice the plug usually is handled manually, obviously a laborious operation. Previous plugs with which I am familiar are of short length and remain stationary during actual rolling operations. Consequently all the wear is in the same narrow band around the plug and its life is short.

An object of the present invention is to provide a simplified and practical mechanism and method for mechanically handling plugs in a plug rolling mill.

A more specific object of the invention is to provide an improved and simplified mechanism and method for mechanically removing plugs from the plug or mandrel bar of a plug rolling mill after each pass of a billet through the roll stand and supplying a cooled plug thereto for the next pass without obstructing the billet as it backs out of the roll stand.

A further object is to provide an improved plug rolling mill and method in which the plug continuously advances counter to the billet as rolling proceeds so that wear is distributed along the plug length and the inside of the billet always is rolled against a cooled fresh plug surface.

A further object is to provide an improved plug rolling mill equipped on its entry side with a rotatable magazine which is adapted in sequence to receive the plug after each pass, furnish a path through which the billet can back out of the roll stand, and then supply a cooled plug for the next pass.

A further object is to provide in a plug rolling mill means for extracting plugs from the plug or mandrel bar after each pass of a billet through the roll stand, a magazine for receiving plugs from the extracting means, and a means for turning the magazine first to furnish a path through which the billet can back out of the roll stand and then to supply a cooled plug for the next pass.

A further object is to provide a plug rolling mill in which the supporting means for the plug or mandrel bar advances this bar continuously counter to the billet during 2,771,800 Patented Nov. 27', 1956 TCQ the rolling operation, and at the conclusion of a pass the plug is removable from the entry side of the roll stand.

in accomplishing these and other objects of the invention, I have provided improved details of structure, a preferred form of which is shown in the accompanying drawings, in which:

Figures 1 and la together are a top plan view, partly in section, of a plug rolling mill which embodies features of the present invention;

Figures 2 and 2a together are a side elevational View, partly in section, of the mill;

Figure 3 is a side elevational view, partly in section, showing the mechanism at the entry side on a larger scale;

Figure 4 is a vertical cross sectional view taken on line IV-iV of Figure 3;

Figures 5 and 6 are vertical cross sectional and longitudinal sectional views respectively taken on lines V-V and \/iVI of Figure l, but on a larger scale;

Figure 7 is a vertical cross sectional View taken on line VII-VII of Figure 6; and

Figure 8 is a diagram of the electrical and hydraulic circuits used in the mill.

Figures 1 and 2 show a plug rolling mill, the roll stand of which includes the usual housings 10, upper and lower chocks 12 and i3 and upper and lower grooved work rolls M and 15. These rolls customarily have several mating sets of grooves Ma and 15a which furnish alternative passes for the work. A trough 16 on the entry side of the roll stand receives pierced and reheated billets B for introduction to the rolls. On its underside said trough is supported on flanged wheels 17, which ride on transverse rails 18. Thus the trough, although normally stationary, can be shifted laterally into alignment with any set of grooves 14a, 15a. Ahead of the trough the mill has a pusher of any standard or desired construction, not shown, for pushing billets into the rolls. On its delivery side the mill has a mandrel bar 19 which has a socket 20 in its end face for removably supporting a plug 21. This plug differs from usual plugs in that it is much longer and on its front end carries a knob 22 for engagement by a gripper of the handling mechanism hereinafter described. The plug has a smaller outside diameter than the inside diameter of the bore through the billet. Therefore the billet is rolled down on the plug and the plug can slip through the unrolled portion of the bore. The mill also has on its delivery side the usual stripper rolls 23 and 24 which are shown only diagrammatically.

Plug bar supporting mechanism Figures la and 2a show the mechanism for supporting and moving the plug bar 19. This mechanism includes a normally stationary frame 25, which can be shifted transversely to align the plug bar with any set of roll grooves 14a, 15a in the same fashion as the trough 16. Frame 25 carries a double acting hydraulic cylinder 26. Pipes 2'7 and 28 are connected to said cylinder adjacent its back and front ends for admitting and discharging hydraulic fluid. A plunger 29 is mounted for reciprocable movement in cylinder 26 and preferably has a greater efiective area on its back face than on its front face. This arrangement enables the plunger to push the plug bar and plug counter to and through the pierced billet slowly and with great force and to retract the plug bar more rapidly. The forward end of the plunger carries an open ended cup 30 and a crosshead 31. A connecting rod 32 is received in said cup, extends through said crosshead and at its forward end is coupled to the rearward end of the plug bar 19. Preferably the connecting rod and plug bar are water cooled, the former having connections 33 and 34 for introducing and discharging cooling water.

A compression spring is inserted in cup 30 behind the end of the connecting rod and permits slight relative longitudinal movement between the connecting rod and the cup. A normally open limit switch 36 is mounted on the crosshead 31 and an actuator 37 for said limit switch is mounted on the connecting rod 32. At the start of a rolling operation plunger 29 is fully retracted in its cylinder 26, but since there is no substantial pressure on the plug 21, the actuator 37 does not close limit switch 36. Pressure of a pierced billet against the forward end of the plug 21 produces suflicient relative movement between the connecting rod and crosshead for the actuator to move back far enough to close this limit switch, whereupon an electric circuit acts to start flow of hydraulic fluid into the back end of cylinder 26 via pipe 27 and thereby to advance the plug bar and plug counter to the billet. The pressure during rolling holds this switch closed. The details of the electric and hydraulic circuits are fully described hereinafter.

Crosshead 31 is slidably received on a pair of longitudi nally extending guide rods 33, which are fixed to the frame 25. Said rods carry adjustable stops 39 and an adjacent their back and front ends. The crosshead abuts these stops at the ends of its stroke to limit positively the end positions of the plug bar and plug. Thus at the conclusion of a pass the plug always occupies the same position at which it can be engaged by the handling mechanism hereinafter described.

Crosshead 31 also carries a longitudinally extending stroke control rod 41. Front and back limit switch actuators 42 and 43 are adjustably mounted on said rod. A pair of mounting plates 44 and 44:: are fixed to frame 25 beneath rod 41 and carry respectively a normally closed front limit switch 45 and a normally open back limit switch 46. The stroke control rod of course moves with the plunger 29, crosshead 31 and plug bar 19. When these parts move ahead to advance the plug during a rolling operation, the back limit switch actuator 43 ultimately reaches the back limit switch 46 and closes it, Whereupon the circuit acts to stop delivery of hydraulic fluid through the pipe 27 to the back of cylinder 26. When the aforementioned parts move back to retract the plug preliminary to starting a rolling operation, the front limit switch actuator 42 ultimately reaches the front limit switch 45 and opens it, whereupon the circuit acts to stop delivery of hydraulic fluid through the pipe 28 to the front of cylinder 26. This action is fully explained hereinafter in the description of the circuits.

Cooling bosh Referring again to Figures 1 and 2, the trough 16 on the entry side terminates somewhat short of the roll stand. A cooling bosh 48 is situated in the intervening space. Said bosh, its operating mechanism, and the plug handling mechanism, hereinafter described, are mounted on a base plate 49 which extends under trough 16 and is bolted at one end to the frame which carries said trough, as indicated at 59, and at the other end to a laterally shiftable stand 51. Thus the bosh and the plug handling mechanism along with the trough 16 can be aligned with any set of roll grooves 14a, 1511. As best shown in Figures. 5 and 7, the bosh has a cooling water inlet 52 and outlet 53 and contains water to a level about as indicated. On its end wall adjacent the roll stand the bosh carries a bottom inlet guide 54 for directing billets into and out of the roll pass (Figures 2 and 3). The two end walls of the bosh contain aligned bearings 55 and 56 (Figure 3) within which a magazine 57 is rotatably mounted so that it can turn on a horizontal axis longitudinally of the trough 16. The magazine has four radially extending partitions 58 (Figures 5 and 7) and the spaces between said partitions furnish four trough extensions 58a, 58b, 58c and 58d.

The magazine 57 has a drive which turns it in quarter revolution steps clockwise as viewed in Figure 5. Whenever the magazine stops, one of the four trough exten sions faces upwardly and is aligned with the trough 16. Referring to Figures 3 and 5, the drive illustrated includes a shaft 59 rotatably mounted in bearings 60 and 61 which are carried on the base 49 ahead of the bosh 38 directly beneath the trough 16. A gear 62 is keyed to the inner end of shaft 59 and a pinion 63 to the outer end of the magazine shaft. Preferably the ratio of gear 62 to pinion 63 is 2 to 1 so that shaft 59 turns only oneeighth of a revolution while turning the magazine onequarter of a revolution. A ratchet wheel 64 is keyed to shaft 59 intermediate the bearings 60 and 61. A bifurcated pawl lever 65 is rotatably supported on shaft 59 and straddles the ratchet wheel 64. Lever 65 carries a pawl 66 which engages the teeth of the ratchet wheel. When lever 65 turns counterclockwise as viewed in Figure 5, it acts through the pawl and ratchet to turn shaft 5? in the same direction and thus turns magazine 57 clockwise. When lever 65 turns clockwise to reset, the shaft magazine remain stationary.

The means for operating the pawl lever 65 includes a double-acting fluid pressure cylinder and piston 67 supported on trunnions 68 situated on the base 49 at one side of the shaft 59. A piston rod 69 extends from this cylinder and is pivoted to the end of lever 65, as indicated at 717. The cylinder is set to turn the pawl lever and shaft one-eighth revolution on each outward stroke of the pis- 110m.

Preferably the outer end of shaft 59 carries means to prevent unintended rotation of the magazine. As best shown in Figure 4, this means includes a circumferentially notched lock wheel '71 keyed to the end of the shaft and a lock bar 72 pivoted to lugs 73 upstanding from the base 49. A compression spring 74 urges the free end of said lock bar upwardly. Intermediate its length the lock bar carries a roller 75 which is engageable with the notches of the lock wheel 71. Such engagement prevents rotation of the magazine unless the cylinder and piston 67 forcibly turn the shaft 59.

The mill utilizes two similar plugs 21 and 21a, one of which cools in the bosh 43 while the other is used in a rolling operation. The two plugs are substantially alike, except that plug 21a used for the second pass can be of slightly larger diameter than plug 21 used for the first pass. Before the start of the first pass of each billet through the mill, the trough extension 58:: faces upwardly and contains the previously cooled plug 21, which is long enough to lie horizontally therein and not become cocked (Figure 3). The trough extension 580 faces downwardly within the cooling bosh 48 and contains the plug 21a. The trough extensions 53/) and 58d face sideways and are empty. At this stage the plunger 2? is fully advanced in cylinder 26, so that the end of the plug bar 19 lies approximately between the work rolls 14 and 15, its position being controlled by engagement of crosshead 31 with stop it) and closing of the back limit switch 46 by its actuator 43. The handling'mcchanism, hereinafter described, next pushes the plug 21 toward the work rolls and the plug bar until the plug on gages the socket 20 of the latter (Figures 1 and 2). Now the plug lies substantially within the bottom inlet guide 54. Next the hydraulic circuit to cylinder 26 is actuated manually to introduce hydraulic fluid through the pipe 23 to its front end and thus retract the plunger 29, ing bar 19 and plug 21. When these parts are fully to tracted, as controlled by engagement of crosshead 31 with stop 39 and opening of the front limit switch #5 by its actuator 42, the forward end of the plug 19 lies approximately between the work rolls 14 and 15. It is to be noted that Figures 1 and 2 show the plug bar 19 fully advanced, while for greater clarity Figures in and 2a show the plunger 29 fully retracted.

Next the billet pusher, not shown, is actuated to push a pierced billet B along the trough 16 through the trough extension 5801 and into engagement with the plug and work rolls in the usual fashion. The billet pushes the plug back slightly, as already described, and thus closes the limit switch 36, whereupon the plug commences to advance counter to the movement of the pierced billet. The advancing stroke of the plunger 29 is completed just prior to the complete rolling of the billet, leaving the plug always in the same place substantially within the guide 54. The plug handling mechanism next returns the plug 21 to the trough extension 58a of the magazine 57.

Plug handling mechanism Referring principally to Figures 1, and 6, the plug handling mechanism includes a shaft 811, which is rotatably mounted in bearings 81 and 82 at the upper ends of a pair of spaced apart pedestals 83 and 34 upstanding from the base 49 on the opposite side from cylinder 67. A carriage 85 is slidably keyed to shaft 81] but rotates therewith. A fluid pressure cylinder 86 is bolted to the underside of the free end of the carriage and contains a reciprocable double-acting piston 87, which has a piston rod 88 extending toward the roll stand (Figure 3). This cylinder and piston act as a pusher for pushing a plug 21 or 210 from the magazine 57 into engagement with the plug bar 19, as already described. A plug gripper 89 is pivoted to the end portion of cylinder 86 toward the roll stand to turn on an axis which is horizontal when the carriage is lowered.

Figures 1 and 3 show the details of a preferred form of gripper 89. This gripper includes two spaced apart plates 90, which have pivot openings 91 adjacent their back ends and hook portions 92 adjacent their front ends. A cross bar 93 holds said plates in spaced relation. The hook portions 92 are adapted to engage the knob 22 on the plug 21 or 21a. The cross bar 93 slopes downwardly toward the roll stand and functions as a cam surface engageable by the end of the piston rod 88 so that the latter can push the gripper up out of the way as it pushes a plug into engagement with the plug bar. The back ends of the plates have horizontal surfaces 94 which are engageable with lugs 95 on the sides of cylinder 86 for holding the gripper in a horizontal position when the piston rod 88 is retracted within said cylinder.

The means for rotating shaft 30 and thus raising or lowering the carriage 85 and gripper 89 includes a doubleacting fluid pressure cylinder and piston 96 suported by the base 49 on trunnions 97 (Figures 5 and 6). A piston rod 98 extends from this cylinder and is pivoted at its free end to a lever 99. Said lever is keyed to the end portion of shaft 89. It is seen that retraction of the piston rod 98 Within the cylinder turns shaft 80 counterclockwise as viewed in Figure 5 and thus raises the carriage 85, while movement of this piston rod outwardly from the cylinder does the reverse.

The means for sliding the carriage 85 along the shaft 80 includes a' double-acting fluid pressure cylinder and piston 105 (Figures 1 and 6) secured to the base 49 alongside the cooling bosh 48. A piston rod 196 extends from the end of this cylinder away from the roll stand and at its free end carries a yoke 107 (Figures 6 and 7). The lower end of this yoke is slidably supported on a horizontally extending rod 108 which is fixed to the base 49 beneath the piston rod 106. The upper end of this yoke is bifurcated, as indicated at 109. Carriage 85 has an arcuate flange 111) which rotatably fits within this bifurcation. It is seen that movement of the piston rod 106 in or out of its cylinder moves the yoke 107 and consequently shifts the carriage 85 along shaft 80.

Preliminary to removing the plug 21 from the guide 54 back to the trough extension 58a of the magazine 57 after a pass, cylinder 195 is actuated to slide the carriage 85 as far as possible toward the roll stand, as shown in Figure 1. Next cylinder 96 is actuated to lower the carriage and the plug gripper 89 over the knob 22. of

the plug 21, as shown in Figure 2. Piston rod 88 is of course retracted at this time. Next, to move the plug, cylinder 105 is actuated to move the carriage in the opposite direction away from the roll stand and thus to pull the plug 21 into the trough extension, as shown in Figure 3. When the plug arrives at the desired position therein, cylinder 105 is stopped, and cylinder 96 is actuated to raise the carriage out of the way and thus to lift the plug gripper 89 from the knob 22, as shown in dot-dash lines in Figure 5.

After the first pass of a billet through the roll stand, the billet is of course situated on the delivery side of the roll stand. Next in the operation of the mill, cylinder 67 is actuated to turn the magazine 57 one-quarter revolution in the fashion already described. One of the empty trough extensions 58b thus moves into alignment with the roll pass. The work rolls 14 and 15 are separated and the stripper rolls 23 and 24 actuated to back the pierced billet from the delivery side to the entry side, as commonly practiced in the art. The billet travels unobstructed through the empty trough extension 58b into the trough 16, where usual handling mechanism, not shown, turns it on its longitudinal axis for the start of another pass. Next the cylinder 67 is actuated to turn the magazine 57 another quarter revolution so that its trough extension 580 moves into alignment with the trough 16 and the roll pass. This trough extension contains the cooled plug 21a which is used in rolling the billet through the next pass. Trough extension 58a of the magazine now faces downwardly and thus plug 21 cools in the bosh 48. The operation already described is repeated, except that the two plugs are reversed and the billet subsequently backs out through the other empty trough extension 58d.

Operating circuits It is seen that the magazine and plug handling could be operated automatically and in sequence by an appropriate system of limit switches. However, I prefer instead to equip the piping to each of the cylinders 67, 36, 96 and with manually operable valves, so that the various movements can be closely controlled by the oper ator. For simplicity l have omitted a detailed showing of these valves.

Figure 8 shows schematically the electric and hydraulic circuits for delivering fluid to and relieving cylinder 26 and thereby operating the plunger 29. The hydraulic circuit includes a solenoid operated four-way valve 120, which has neutral positions. A pipe 121 is connected to said valve and leads to a source of fluid under pressure, and another pipe 122 is connected thereto and leads to a tank or reservoir. Pipes 27 and 28, which lead to the back and front ends of cylinder 26, also are connected to this valve. The valve has an in operating solenoid 123 which, when energized, operates the valve to interconnect pipe 121 with pipe 27 and pipe 122 with pipe 28 and thus to deliver hydraulic fluid to the back of cylinder 26 and relieve the front for advancing the plunger 29. The valve also has an out operating solenoid 124 which, when energized, operates the valve to interconnect pipe 121 with pipe 28 and pipe 122 with pipe 27 and thus to deliver hydraulic fluid to the front of cylinder 26 and relieve the back for retracting the plunger. When neither solenoid is energized, the valve automatically returns to a neutral position. Valves of such operation are well known and per se are not a part of the present invention; therefore no detailed showing is deemed necessary.

The electric circuit includes lines 125 and 126 connected to a suitable outside power source through a master switch 127. The circuit also includes an in relay A, an out relay C and a control relay D. The in relay has two sets of normally open contacts 128 connected to opposite sides of the in solenoid 123 and to lines 125 and 126. Likewise the out relay has two sets of normally open contacts 129 connected to opposite sides of 7 the .out solenoid 124 and to lines 125 and 126. Thus when either relay A or C is energized, its normally open contacts close and energize the corresponding solenoid to operate valve 12%. The in" relay A also has 21 normally closed set of contacts 139. The control relay D has two sets of normally closed contacts 1.31 and .132.

Limit switch 256, the coil of the in relay A and the normally closed contacts 132 of relay D are connected in series across lines 125 and 25.26. Thus closing of this limit switch when the end of a pierced billet pushes against the plug 21 or 21a completes the circuit through the relay coil, energizes solenoid 123 and operates valve 12% to advance plunger 26. The normally open back limit switch 56 is connected in series with the coil of control relay D across lines 123 and P6. When the actuator 43 closes this switch 46 on completion of the plunger stroke, relay D is energized and its normally closed contacts 131 and 132 open and break the circuit to the coil of relay A. This relay and the solenoid 123 which it controls consequently are tie-energized and valve 12% returns to its neutral position.

The normally closed contacts 139 of the in relay A, the normally closed front limit switch 45, the coil of the out relay C and the normally closed contacts 131 of the control relay D are also connected in series across lines 125 and 126. A normally open manually actuated out" switch 33 Dy-passes contacts 131. As long as the in relay A is energized, the out" relay C is tie-energized since contacts are open. When the plunger 29 reaches its most advanced position and the in relay is rte-energized, the out relay remains tie-energized, since contacts 131 open as the control relay D is energized, thus assuring that the valve 129 stays in its neutral position.

After the plug 21 or 21a has been advanced into engagement with the plug bar 19, the operator manually closes the out switch 133, which completes the circuit through the coil of the out relay C and thus energizes solenoid 12 i. Valve 120 now admits hydraulic fluid to the front of cylinder 26 and retracts plunger 29. As the plunger commences to move back, the back limit switch 45 returns to its normally open position, again tie-energizing the control relay D. Contacts 131 and 132 close; the former complete a current path to the coil of relay C, shunting the switch 133, and the latter set up, but do not as yet complete, a current path to the coil of relay A.

The plunger continues to move into the cylinder until the front limit switch actuator 42 engages and opens the normally closed front limit switch 45. Opening this switch breaks the circuit to the coil of the "out relay C. This relay and the solenoid 124, which it controls, consequently are d e-energized and valve 124) returns to its neutral position. The circuit to the coil of relay C is reset when the plunger again moves forward and the normally closed switch 45 again closes.

From the foregoing description it is seen that the present invention affords a simple and reliable mechanism and method for handling and cooling plugs mechanically. At the same time the continuous advance of the plug during a rolling operation always insures that the pierced billet is rolled against a fresh plug surface.

While l have shown and described only a single embcdiment of the invention, it is apparent that modifications may arise. Therefore, I do not wish to be limited to the disclosure set forth but only by the scope of the appended claims.

I claim:

1. A plug rolling mill adapted to roll reheated and pierced billets comprising at least one roll stand, a trough on the entry side of said roll stand in alignment therewith and adapted to receive work for rolling, a longitudinally movable plug bar supported in alignment with said roll stand and trough, a plug carried by one end of said plug bar and having an elongated bearing surface, stop means which initially positions said plug bar and plug with the forward end of the plug within the roll stand and which iii) limits movement of said plug bar from said roll stand, motive means for continuously advancing said plug bar and plug through said stand during a'ro'lling operation in a direction counter to that in which the work travels therethrough and continuously presenting a fresh surface of the plug to the portion of the work which is moving within said roll stand, means for actuating said motive means and starting said plug bar and plug in motion when the work engages the forward end of the plug, and means for stopping the advance of said plug bar and plug when the back end of the latter is within said roll stand at the end of the rolling action, thereby preventing the work from seizing on the plug.

2. A mill as defined in claim 1 in which the actuating means for said motive means includes a pressure operated electric switch actuated by engagement of a billet with the plug and connected with said motive means.

3. A Plug rolling mill adapted to roll reheated and pierced billets comprising opposed work rolls having grooves adapted to encompass the outside of a billet as the millet travels between the rolls, a trough on the entry side of the rolls adapted to receive billets for rolling, a longitudinally movable plug bar supported in alignment with said grooves and trough, a plug carried on said plug bar and having an elongated bearing surface adapted to engage the interior of the billet, stop means which initially positions said plug bar and plug with the forward end of the plug in the grooves between rolls and which limits movement of said plug bar away from the rolls, motive means for continuously advancing said plug bar and plug through the grooves during a rolling operation in a direction counter to that in which a billet travels therethrough and continuously presenting afresh surface of the plug to the portion of the billet which is moving between rolls, means for actuating said motive means and starting said plug bar and plug in motion when the billet engages the forward end of the plug, and means for stopping the advance of said plug bar and plug when the back end of the latter is within the grooves between rolls at the end of the rolling action, thereby preventing the billet from seizing on the plug.

4. A plug rolling mill adapted to roll reheated and pierced billets comprising opposed work rolls having grooves adapted to encompass the outside of a billet as the billet travels between the rolls, a trough on the entry side of the rolls adapted to receive billets for rolling, a fluid pressure cylinder, 21 plunger in said cylinder, a plug bar connected to said plunger for longitudinal movement therewith and supported in alignment with said grooves and trough, a plug carried on said plug bar and having an elongated bearing surface adapted to engage the interior of a billet, a crosshead connected to said plunger for movement therewith, a first stop with which said crosshead is engageable to position said plug bar and plug initially with the forward end of the plug in the grooves between rolls, means for admitting fluid to said cylinder to move said plug bar and plug continuously through the grooves in a direction counter to that in which the billet travels therethrough and thus continuously presenting a fresh surface of the plug to the portion of the billet which is moving between rolls, means for actuating said cylinder and starting said plug bar and plug in motion when the billet engages the forward end of the plug, and a second stop spaced from said first stop and with which said crosshead is engageable for stopping movement of said plug bar and plug when the back end of the latter is within the grooves between rolls at the end of the rolling action, thereby preventing the billet from seizing on the plug.

5. A mill as defined in claim 4 in which the means for actuating the cylinder includes a presure operated electric switch between said plug and said plunger, and a solenoid operated valve connected to said switch for conrolling admission of fluid to said cylinder.

(References on following page) References Cited in the file of this patent UNITED STATES PATENTS King Jan. 27, 1903 King Oct. 6, 1903 Nowak Aug. 20, 1912 Valerius Apr. 28, 1914 Ofiutt June 16, 1914 Matheson May 8, 1923 Liddle Apr. 8, 1930 10 10 Lowy June 17, 1930 Judson May 30, 1933 Bark June 18, 1935 Gettig Apr. 21, 1953 FOREIGN PATENTS Germany Nov. 15, 1913 Germany Jan. 23, 1932 Germany Jan. 15, 1935 

